Automotive Paint & Coating Defects
Below is a list which explains the major automotive paint defects you may experience, what causes them, how to prevent them, and the solutions so you can be sure you achieve a perfect finish every time. While these answers are specifically based on the ProMix ECLIPSE range, the defects and the rectifying solution will work on all types of automotive paints. If you are not seeing the defect you are experiencing, send us a question using the link below and one of our team will be back in touch to help out as soon as possible.
Poor Clearcoat Adhesion Can Occur If:
- The basecoat is too thick.
- There has been too long a delay between final basecoat and 1st coat of clearcoat.
- Flash off times of the basecoat were too short ( intermediate & final flash times).
- The mixing ratios of the clearcoat and hardener are not correct.
- There is contamination present on the surface of the basecoat before clearcoat is applied. (This includes any foreign material such as dust, moisture, finger marks etc. )
How To Prevent Poor Adhesion:
- Keep your basecoat spray passes to 3 passes max.
- Read the instructions and follow the directions regarding the basecoat flash times.
- Limit the time between the last coat of basecoat and 1st coat of clearcoat. (If there is an unavoidable delay, we recommend sanding, cleaning and respraying the basecoat before applying the clearcoat.)
- Follow the clearcoat manufacturers recommended hardener to clearcoat mixing ratios.
- Keep the car/part/item being worked on in a clean area to reduce the chance of contamination before clearcoat is applied.
Unfortunately, poor clearcoat adhesion has to be remedied by sanding and repainting to effectively solve the issue and give a professional finish.
Atmospheric Dust Drying on Painted Surface
What Does Atmospheric Pollution Feel Like on Paint?
This can cause the finished paint to be rough or ‘gritty’ to the touch.
What Causes Atmospheric Pollution?
This defect can be caused when there are particles of dust, ash, or other pollutants airborne in the painting and/or drying environment.
How To Prevent Atmospheric Pollution:
While this may not be possible for all car bodywork shops, we would suggest that where possible, the painting and drying areas are shut off from the outside air to avoid pollutants. Dampening the floor with water can help reduce airborne dust particles, depending on their size.
The remedy to this annoying paint surface defect depends on the severity and depth of the problem. In cases where the pollutants have not penetrated the paint, but merely are surface contamination, the surface may be restored by light sanding and polishing.
In cases of heavier contamination, the only solution is to remove the paint layer using oxalic acid or paint stripper.
Please note that proper PPE must be worn with the use of oxalic acid as this is a poison.
Paint Bleeding Between Layers
Bleeding may occur when the solvent of the new paint being applied dissolves the pigment of the previous paint (or peroxide), revealing its color.
What Causes Paint Bleeding?
- Excessive application of peroxide when using the putty.
- Inadequate blending of the hardener with the putty.
- Failure to isolate or remove delicate colors and types of paint (e.g., red synthetic paint) when applying a potent solvent on top.
- Insufficient cleaning.
- Contamination of the ground coat due to a product that tends to manifest this issue.
How To Prevent Paint Bleeding:
- Utilize a dispensing machine or a weighing scale (2%) for precise measurement when combining putty and hardener. Over time, professionals will develop an understanding of the appropriate quantity based on the mixture’s color.
- Thoroughly blend the hardener and putty together.
- Take precautions to prevent spray dust of sensitive colors from settling on other vehicles.
- Ensure thorough cleaning of materials.
- Conduct a trial by spraying a small area for testing purposes.
- In certain situations, complete removal becomes necessary.
- Occasionally, this issue may not arise until several layers of car paint have been applied. In such cases, it is essential to fully eliminate the old paint and primer down to the bare metal.
- For instances of peroxide bleeding, the recommended remedial steps involve sanding, isolating the putty filler with GenPox Isolating primer, priming, and painting.
Paint BlisteringThis defect looks, as the name suggests, like blisters or pockets where the paint is affected by moisture on the surface before application of paints.
What Causes Moisture Blisters?
- Any source of moisture on the surface before painting.
- Sanding-water residue
- Water trapped behind trim or decorative strips.
- Contaminated air supply to spray guns or tools.
- Ambient humidity too high.
- Water borne basecoats not completely dried.
How To Prevent Moisture Blisters:
- Ensure the surface is prepped properly and dried with dry air.
- Always remove exterior trim and decorative strips to avoid contamination and moisture retention.
- Inspect air supply to tools regularly and ensure that air supply is dry.
- Ensure basecoats are dry before applying further coats.
- ensure surface is cleaned well.
Cloud-like Paint Finish
Clouding arises due to the uneven dispersion of metallic flakes, resulting in the formation of dark spots known as clouding.
What Causes Paint Clouding?
- Incorrect paint viscosity for spraying.
- Poor technique and/or pressure during spraying.
- Inproper setup of the spray gun.
- Inappropriate choice of thinner.
- Unsuitable spraying temperature.
- Incorrect flash-off time.
How To Prevent Paint Clouding:
- Fine-tune material viscosity, spray gun setup, spraying technique (Maintain a perpendicular angle to the panel), flash-off time, and pressure.
- Utilize the recommended thinner.
- When working with monocoat 2K metallic, it is possible to apply a mist coat immediately after the final spray coat.
Colour Shade Difference
Occasionally, the painter may be unpleasantly surprised to discover that the sprayed panel does not align with the adjacent panel once the masking paper is removed.
What Causes Color Offshade?
- Flawed spraying technique: Application of paint that is either excessively wet or overly dry.
- Improper spray gun configuration.
- Incorrect spraying pressure.
- Insufficient opacity, resulting in poor coverage.
- Weathering causing a change in the original panel color.
- Initial color mismatch or shade discrepancy.
How To Prevent Color Offshade:
- Perform a spray test on a card prior to application.
- Achieve color blending.
- Polish the neighboring panel to verify the color.
- Adjust the color tone, sand, and repaint if necessary.
- Achieve color blending.
Cracks or Ripples
Visible cracks appear in one of the ground coats.
What Causes Cracking or Rippling?
- Variation in solubility between paint films caused by surface aging and hardening.
- Application of a ground coat that has undergone accelerated drying at elevated temperatures prior to polishing and applying the final coat.
- Interlayering of synthetic products like synthetic primers between two layers of nitro-cellulose paint.
- Excessive time lapse before applying the second coat of synthetic paint, resulting in partial drying of the first coat.
- Usage of an inappropriate isolating primer instead of removing the old paint.
- Aggressive solvents in the topcoat attacking a heavily applied synthetic primer with insufficient or no flash-off time between coats.
The likelihood of cracking is heightened when applying thick, wet layers of synthetic paint. Cracking commonly occurs due to variations in flexibility between two types of finishes, with the first coat being more flexible than the second coat.
How To Prevent Cracking Or Rippling:
- Thoroughly sand the existing paint prior to painting (in certain instances, isolate or remove old paint).
- Ensure that the surface temperature matches the ambient temperature before painting.
- Avoid applying thick coats.
- Never layer a synthetic product between two coats of nitro-cellulose (NC) paint.
- Conduct a solvent test.
- Ensure adequate drying time.
- For severe cases, it may be necessary to sand down to the bare metal, clean using Valox, and apply a fresh coat.
- In minor cases, particularly with T.P.A (Thermoplastic Acrylics), you can use P1200 sandpaper to sand and then polish the affected area.
Paint Drying Too Slowly
What Cases Slow Drying?
- Excessive thickness of the paint, leading to external drying while trapping solvents in the paint film.
- Application of paint over surfaces contaminated with wax, oil, or grease.
- Poor drying conditions, such as a cold, humid, and poorly ventilated workshop.
- Inadequate application conditions, including insufficient air circulation and heat.
- Insufficient flash off time.
- Excessive use of retarder.
- Incorrect choice of hardener or improper mixing ratios.
How To Prevent Slow Drying:
- Thoroughly clean the surface before painting to remove any contaminants.
- Avoid applying thick layers of paint.
- Improve spraying and drying conditions by ensuring proper heat and air circulation.
- Allow sufficient time for flash off between coats.
- Use the recommended hardener and thinner, and follow the specified mixing ratios.
In most cases, a slow drying problem can be addressed by moving the vehicle to a location with better ventilation and appropriate temperature, or by applying moderate heat (unless the issue stems from using an incorrect hardener or improper mixing ratio). If the problem is caused by excessively thick layers, the appearance of wrinkles (“des rides”) may occur unless special care is taken during the heating process.
This is where the paint exhibits cratering, characterized by varying thickness, density, and sizes of craters ranging from small pinholes to 1 cm in diameter. Upon closer examination using a magnifier, a tiny impurity can be observed at the center of each crater.
What Causes Fish Eyes?
- Presence of wax, silicone, oil, or grease contamination.
- Residue contamination from soap, detergents, or metal cleaning products.
- Air contamination from the nearby vicinity of a mechanic shop.
- Contamination of the air supply.
- Contamination caused by the use of polishes or aerosol sprays containing silicone.
How To Prevent Fish Eyes:
- Ensure thorough cleaning of the surface after each operation using Genclean 8281. Employ a fresh cloth for each vehicle.
- Take precautions to utilize silicone-containing products as far away from the workshop as feasible.
- Apply a mist coat.
- Sand the panel, isolate it, and proceed with repainting.
- Consider using antisilicone 8678 as a final option.
What Causes Low Gloss?
- Improper use of thinner.
- Surface contamination prior to painting.
- Excessive air pressure.
- Inadequate extraction and airflow in the spray booth, leading to settling of paint-generated dust on the drying surface.
- Drying of paint in the presence of exhaust or industrial fumes.
- Inadequate drying conditions, such as low temperature, high humidity, or insufficient ventilation.
- Incorrect mixing ratios of hardener and thinner, deviating from the manufacturer’s specifications.
- Application of an excessive number of coats.
- Insufficient flash-off time between coats.
- Insufficient stirring of a highly pigmented ground coat before application.
- Use of unsuitable sandpaper grade.
- Sanding the ground coat before it is fully dry.
- Expired or damaged hardener, affected by humidity when the can is left open.
How To Prevent Low Gloss:
- Utilize the recommended thinner.
- Thoroughly clean the surface prior to painting.
- Adhere to the correct mixing ratios.
- Employ the appropriate pressure for spraying.
- Regularly inspect the air flow of the spray booth.
- Maintain a warm workshop environment during winter.
- Ensure complete drying of the paint before proceeding with polishing or considering a respray.
‘Orange Peel’ Finish
The ‘Orange Peel Effect’ is a defect that gets it’s name from the way the paint appears to have the texture of the outside of an orange.
What Causes Orange Peeling?
- Incorrect spray gun pressure or viscosity
- Incorrect spraying technique
- Application temperature outside of manufacturer recommendations
- Solvents used are not compatible or solvent is low quality.
- Base coat or base is not sanded well enough.
- High temperature application environment.
How To Prevent Orange Peeling:
- Carefully follow all paint manufacturer application directions from data sheets.
- Make sure base coat or surface to be painted is well prepared and dust free.
- Ensure spray gun is set up correctly for the paint being used.
- Test on a small area first.
- Always use recommended or high quality thinners
- Avoid painting in environments where the temperature is high.
The solution to this problem is unfortunately to re-sand and repaint the surface ensuring that all the correct procedures are followed and the preventative measures listed above are observed.
This defect looks like drips or runs of paint downward on the surface painted.
What Causes Paint Runs Or Drips?
- Incorrect viscosity of the paint.
- Paint film to thick and as a result the force of gravity causes the runs.
- Inconsistent film thickness, too thick in some places.
- Spraying pressure not correct causing incomplete atomisation.
- Temperature of surface being sprayed, environment, or paint is too low.
- Incorrect hardeners or thinners used.
How To Prevent Paint Runs Or Drips?
- Ensure the paint is the correct viscosity.
- Ensure spray gun is setup correctly and is spraying evenly.
- Ensure surface and environment is at least 20℃ / 68℉
- Follow all manufacturer instructions.
- Use correct and recommended hardeners and thinners.
This is another defect that the solution depends on the severity.
For minor defects, sanding with a fine grit and polishing may fix the defect.
For more severe defects, sanding and repainting is the recommended solution.
What Causes Pinholing?
- Applying a colored coat on a dry ground coat results in the formation of air bubbles due to factors such as high viscosity, low air pressure, or high ambient temperature, causing rapid drying.
- Inadequately sanded old pinholes are present.
- The putty has been applied poorly.
- Fiberglass bodies are involved.
- The polyesters were not mixed thoroughly enough.
- The polyesters were not primed sufficiently.
How To Prevent Pinholing:
- Prevent the occurrence of spray dusting by applying initial coats carefully.
- Follow the recommended viscosity (thinning ratios) and air pressure guidelines.
- Thoroughly sand the ground coats.
- Employ the proper technique while applying putties. Hold the knife at a 60-degree angle to prevent rolling of the putty and the formation of air bubbles.
- Ensure thorough mixing of polyesters.
- Whenever feasible, utilize polyester spray filler (574 with H353 hardener).
- Make sure to fill the polyesters adequately.
- Eliminate the damaged finish.
- Sand the surface and apply polyester spray filler (574).
- Apply primer and paint.
After the polishing process, visible marks or swirls from sanding are apparent.
What Causes Polish Marks?
- Insufficient drying of the topcoat.
- Usage of excessively coarse sanding paper.
- Inappropriate choice of polish.
- Unsuitable equipment for polishing.
- Over-polishing on edges.
How To Prevent Polish Marks:
- Ensure thorough drying of the topcoat, and consider additional baking if needed.
- Utilise suitable polish and equipment for the task.
- Select appropriate sandpaper with the right level of coarseness. Don’t skip grades of sandpaper, increasing the grade by no more than double at each sanding stage, eg 600, 1200, 2400 grit
- Use a car-paint polish that does not contain ammonia.
- Thoroughly dry the topcoat.
- Sand, polish, or repaint as necessary.
Poor opacity simply means that the old paint or basecoat is visible through the topcoat.
What Causes Poor Opacity?
- The topcoat was not stirred and mixed well before applying.
- The topcoat was thinned too much.
- The incorrect thinner was used.
- The film build is too low resulting from not enough spray passes.
How To Prevent Poor Opacity:
- Ensure that the paint has been stirred/mixed well.
- Follow the manufacturers advice on thinning especially the ratios.
- Ensure the correct thinner is used for the topcoat.
- Apply enough topcoat to achieve the required opacity.
The solution to this defect is to allow the topcoat to fully dry, and then resand, prep and respray with the correct thinner, ratio, and spray passes.
Powder-like paint dust particles land on the painted surface during spraying.
What Causes Poussierage?
- Spray gun held too far from the painted surface.
- Quick movement during the spray pass.
- Use of unsuitable thinner.
- Excessively high air pressure.
- Incorrect application viscosity.
- Incorrect spray gun settings, such as using a small nozzle with a large air cap.
- Disruptive ambient air flow.
- Excessive temperature in the spray booth.
How To Prevent Poussierage:
- Use proper application technique, maintaining an appropriate distance between the spray gun and the surface.
- Select the appropriate thinner for the paint.
- Use the correct air pressure during spraying.
- Follow the manufacturer’s specification for the recommended application viscosity.
- If the temperature is too high, consider using a slower thinner or adding a retarder.
- Ensure the spray gun is correctly set up.
- Avoid turbulence or disruptive air flow in the working area.
- For ground coats, remove the powder-like particles with appropriate thinner, or wait until the surface is dry and sand it with P1200 sandpaper, followed by polishing.
- In the case of metallic monocoat finishes, sand the affected area and then respray to achieve a proper finish.
Rust In Newly Painted Surfaces
What Causes Rust?
- Water contacting the metal surface, leading to paint film imperfections.
- Inadequate removal of rust before applying the paint.
- Surface contamination, such as finger marks, dried water spots, or delay between cleaning with a phosphoric acid-based product and spraying with protective paint layer.
Rust issues are particularly noticeable in regions where salt is used on the streets during the snow season.
How To Prevent Rust:
- Thoroughly remove all traces of rust before painting.
- Take precautions to avoid any surface contamination prior to spraying.
- Sand the affected area down to the bare metal, ensuring the sander reaches the rusty paint until the surface is clean and brilliant.
- Use a product like Valox, which is based on phosphoric acid, or utilize sandblasting to thoroughly clean the surface.
- Repaint immediately after completing the remedial steps.
Sanding marks can be seen in the finished paintwork.
What Causes Sanding Marks?
- The basecoat has been applied too thick.
- The basecoat has not been given enough drying time before the topcoat is applied.
- The final grit of sand paper used for prep was too coarse.
- The basecoat is sensitive to the solvents used in the topcoat.
- The film build of the topcoat is too low.
How To Prevent Sanding Marks:
- Ensure that your basecoat and substrates are completely dry before applying topcoat.
- Allow sufficient time between coats.
- When sanding, use a finer grit to ensure marks from coarser grits have been removed before applying topcoat.
- Test the solvents on a test piece before applying to a production piece.
- Apply the recommended or required thickness of topcoat.
Wet-sanding reduces friction and clogging, resulting in smoother finishes when using P1200 grit or above grade.
When two adjacent substrates react differently to the solvents in the topcoat or when there is a variation in roughness between the two substrates, shrinkage or edge mapping occurs.
What Causes Shrinkage/Edge Mapping?
- Failure to isolate the area or use an inappropriate filler for isolation.
- Incorrect application of the filler.
- Incorrect mixing ratio, applying the topcoat too thinly, or excessive sanding that exposes the substrate.
- Insufficient drying or curing of the substrate.
- Excessive thickness of the topcoat film.
- Usage of overly coarse sanding paper.
How To Prevent Shrinkage/Edge Mapping:
- Conduct a solvent test to identify soft substrates before application.
- Avoid applying thick coats of filler without sufficient flash off time, as this can trap solvents within the film.
- Avoid sanding excessively and down to the substrate.
- Apply putty only to bare metal surfaces.
- Apply an appropriate isolating primer and follow the recommended guidelines.
- Ensure proper drying of preparatory materials.
- Thoroughly dry the topcoat.
- Sand the damaged area, isolate it, and then repaint.
- If uncertain, remove all layers down to the bare metal. Apply a wash primer and respray the affected area.
Solvent popping presents itself as micro bubbles on the surface of the paint.
What Causes Solvent Popping?
- If primer filler is not allowed to fully dry.
- Surface preparation solvents are not fully dry before spraying.
- Solvents trapped in paint film escape leaving marks where bubbles have burst. this can be caused by incorrect viscosity, incorrect pressure, flash-off times and drying times.
- Incompatible hardener and thinner mixed.
- Film coat is too high resulting in trapped air/gasses.
How To Prevent Solvent Popping:
- Ensure all surface prep solvents and primer fillers are dry before application.
- Try to avoid air being trapped in coat.
- Use correct and compatible hardeners and thinners.
- Follow manufacturers recommendations.
- Avoid excessive film thickness.
The solution depends on the severity of the defect.
If the defect is minimal, repainting the surface after drying within 24 hrs may solve it.
In more severe cases, re-sanding, prep and repainting is the correct and best way to solve this defect.
“Spider’s Web” Paint Defect
When using a spray gun, the paint is expelled in the form of filaments, resulting in a phenomenon known as “spider’s web” where the filaments are not dissolved in the paint film.
What Causes Spider’s Web?
- Usage of cold paint that has thickened.
- Incorrect pressure settings.
- Very high viscosity of the paint.
- Application of an incorrect thinner.
How To Prevent Spider’s Web:
- Ensure spraying is done at the correct temperature and viscosity.
- Use an appropriate thinner for the paint.
- Reduce the air pressure and/or adjust the viscosity of the paint until the issue is resolved.
Certain products like Body Schutz, polyester spray filler, or textured paint may require a special spray gun equipped with a 3.0 mm nozzle for proper application.
“Salt & Pepper” Paint Finish
This defect, as the name suggests, is the appearance of small black specs in lighter colours, usually only appearing after clearcoat.
What Causes The Salt And Pepper Effect?
- Usually caused by over wetting of metallic basecoats when using water borne basecoats.
How To Prevent The Salt And Pepper Effect:
- To avoid this, make sure that the correct mixing ratio is observed.
- Ensure spray pressure is correct and the correct spray technique is used.
As this defect is usually only noticeable or visible after clearcoat application, sanding and refinishing of the clearcoat and basecoat is required to rectify.
Paint Spray Banding/Strips
There is a noticeable variation in color intensity, with each spray pass appearing separately.
What Causes Striping/Banding?
- Incorrect spraying technique, with inconsistent gaps between the spray passes.
- Spray gun held too close to the panel.
- Spray gun not maintained perpendicular to the panel.
- Incorrect setup of the spray gun.
- Incorrect viscosity and pressure settings during spraying.
- Insufficient flash off time.
- Unsuitable application temperature.
- Unsuitable choice of thinner.
How To Prevent Striping/Banding:
- Utilise the correct spraying technique and ensure proper spray gun setup. Maintain consistent gaps between spray passes (typically starting halfway through the previous pass).
- Follow the manufacturer’s recommendations for mixing ratios and use only recommended thinners for the paint. Adhere to the specified spraying pressure.
If the issue is identified early on (before applying clear coat over the base coat, for example), it can be rectified easily by applying another spray pass. Otherwise, allow the surface to dry completely, sand it, and then repaint as necessary.
Milky White Areas
During application, milky spots become visible on the paint film when the ambient air is highly humid. This occurs due to condensation of atmospheric humidity, which dissolves the components of the paint film when the temperature decreases rapidly due to solvent evaporation.
What Causes Whitening?
- Excessive ambient humidity.
- Usage of low-quality solvents.
- Thinner with a fast evaporation rate.
- Cold temperature in the workshop.
- Weak airflow in the spraying booth.
How To Prevent Whitening:
- Heat the workshop to reduce humidity levels.
- Use a high-quality thinner.
- Add a retarder to the thinner to slow down the evaporation rate.
- Opt for a slower evaporating thinner to counteract the effects of humidity.
- If there are minimal signs of whitening, allow the paint to dry completely and then polish the affected area.
- If the problem is clearly visible, spray the affected region with a slow thinner or retarder.
- In severe cases where water droplets are present in the paint, allow the surface to dry, sand it, and then apply a fresh coat of paint.